As a medium of external storage media such as a personal computer and a multi-function terminal, a multimedia card standardized by the MMCA (MultiMedia Card Association) as the standardization organization is widely known. This multimedia card is used for storing still-pictures of digital cameras, data of a mobile telephone and music of a mobile music player or the like.
A multimedia card is formed of a flash memory and a controller for controlling the same flash memory. The controller is also provided with a power supply voltage detection circuit. This power supply voltage detection circuit detects the rising edge of the power supply voltage supplied from a host machine to thereby perform resetting.
According to investigation by the inventors, the multimedia card is subjected to the so-called power on reset process for initialization of the same card in order to stabilize operation when the power supply voltage is supplied.
This power-on reset process is performed to check whether the flash memory is ready for operation or not, by making access to the flash memory from the controller to read the data in the system region such as CID (Card Identification number register)/CSD (Card Specific Data register) after the power supply voltage detection circuit resets the controller by detecting the rising edge of the power supply voltage supplied from the host machine.
As an example of the document describing details of an IC card of this type, the “Electronic Materials” P22 to P26 edited by Masashi Ohshima and issued by Industrial Investigation Association Co., Ltd. on Dec. 1, 1990 may be listed. This document also describes technical trend of various IC cards.
However, the inventors of the present invention have found problems in the power-on reset processing technology for the memory card as described above.
In general, the operation voltage of the flash memory is set higher than the operation voltage of the controller and therefore here rises possibility that the flash memory does not reach the operation voltage when the controller makes access to the flash memory.
Accordingly, a problem may be assumed to occur in which the flash memory does not operate normally when the controller makes access to the flash memory, the data of the system region such as CID/CSD cannot be read successfully, the controller enters the condition in which the controller cannot accept the commands at all from the host machine, and thereby the host machine can no longer recognize the multimedia card.
An object of the present invention is to provide a memory card which can remarkably improve reliability by surely conducting the power-on reset process even if the power supply voltage supplied is unstable, and to provide a method of initializing the same memory card.
The aforementioned and the other objects and the novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.